linux-kernel - mdadm grow to double the capacity

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Date:   Tue, 26 Nov 2019 02:26:47 +0000
From:   "Paramasivam, Meenakshisundaram" <mparamas@...ui.edu>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: mdadm grow to double the capacity

Hi,

I have raid-6 mdadm array with 8 drives (5 TB each), and a total of 30 TB usable space. XFS is created on this volume. Since I am about 85% used,  I want to add 6 more drives to this existing array in raid-6 to take this array to 60 TB with 14 drives in raid-6.  

What would be the fastest (and safest) way to grow the raid-6 array from 8 disks to 14 disks? I am assuming I can first add the 6 drives, and grow all at once with the command:

mdadm -v --grow --raid-devices=14 /dev/md2

 How long will this take (estimate)? Should I umount xfs before attempting to grow the mdadm array? 

I am aware that I need to grow xfs after the mdadm grow operation. 

Please let me know or point to tips. Thanks.

Sundar